The present invention relates to a bone fixation system, and particularly (though not exclusively) to a system that may be employed in bone implant surgery such as hip replacement operations, or subsequent surgical treatment of the bone structure in the region of an implant. The term “bone fixation” is intended to cover not only the connection of bone to bone but also the connection of components to bone.
More specifically, the invention relates to bone plates that utilize cerclage wire to fix the plate, at least in part to bone. Such devices have been used to reattach trochanteric bone to the femur.
Cerclage is a known fixation technique in which a bone is encircled by a flexible member such as a cable which is drawn tight and clamped. This may serve to hold portions of bone or bone graft together and/or to retain some surgically applied component. For an account of current cable techniques for trochanteric reattachment, femoral allograft fixation and fractures of the proximal femur in revision total hip arthroplasty, the reader is referred to D. M. Dall, Techniques in Orthop. 1991; 6(3):7–16. This describes, among other things, use of a bone fastener for the greater trochanter, as disclosed in U.S. Pat. No. 4,269,180. This known bone fastener is a generally H-shaped implant comprising a base structure including a pair of limbs joined by a bridge, the bridge being bounded by a front face, a rear face and edge faces, a plurality of teeth protruding from the base structure, all the teeth lying on the same side of the base structure, and at least one hole in the base structure for receiving a cable, the hole being elongate in form, extending lengthways through the bridge, and being open at each end. The bridge is adapted to be crimped so that cable(s) can be passed through the hole(s), pulled tight, and then locked by crimping. An A-shaped version of this plate is shown in U.S. Pat. No. 6,066,141. Another bone plate system using a crimpable bridge is shown in U.S. Pat. No. 5,665,089, the teachings of U.S. Pat. No. 5,665,089 are incorporated herein by reference.
FIG. 1 of U.S. Pat. No. 5,665,089 is a drawing, taken from the cited paper, shows a femur 10 that has undergone reconstructive surgery including use of a fastener 12 according to U.S. Pat. No. 4,269,180. In this procedure, the greater trochanter 16 was cut (osteotomised) to facilitate installation in the bone cavity of an internal bone graft 14 and the stem of a prosthesis (not shown). Thereafter the greater trochanter 16 was reattached to the femur 10 by means of the fastener 12 and cerclage cables 18. In addition, a fracture 20 of the femur was surgically treated with a further application of cerclage techniques. Thus elongate medial and lateral bone grafts 22 have been applied to the bone, and bound in place by a multiplicity of cerclage cables 25, each of which has been drawn tight and had its ends locked by crimping in an individual crimp sleeve 26.
A typical prior art plate as shown in U.S. Pat. No. 5,665,089 has a unitary body having the form of a pair of side limbs connected by bridges. Thus, there are defined a plurality of apertures or openings preferably each approximately rectangular in plan. Typically, the bone contacting end of the plate is curved to conform to the surface of the bone to which it is to be applied. Pairs of holes or bores pass through the plate in the region of each bridge.
Each aperture is delimited by a wall that generally extends at right angles to the upper surface of the plate.
As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.